ESTA VISA USA is not a visa but an electronic travel authorization to enter the U.S.A territory. Electronic System Authorization (ESTA) is only for citizens of certain countries benefiting from the visa waiver program.
Also known as E VISA USA, has become mandatory since January 12, 2009. Once your ESTA application is approved, you can enjoy it for multiple entries into the United States.
ESTA application is only one of the formalities which should be fulfilled before going to the USA. Start by filling out the ESTA form before boarding the airplane to U.S.A destination.